The present invention relates to analytical methods of quantitating the non-structural carbohydrate of a feedstuff and has particular utility in determining the non-structural carbohydrate content of both grain and forage components of dairy cow rations.
It is well known, of course, that carbohydrates are the principal energy source for many animals, as well as humans. Plant carbohydrates may be categorized in two major groups, namely, structural and non-structural. The structural carbohydrates, found in the cell wall, are essentially rigid in nature, providing strength to the cell walls and thus to the plant itself. The fibrous materials which make up the cell walls, i.e., the structural carbohydrates, also known as meutral detergent fiber, are mainly cellulose, hemicellulose, and lignin. Non-structural carbohydrates, found mainly within the lumen of the cell, include sugars and starch. Although pectins (D-methyl-galacturonic acid) are a soluble component of the cell wall, they are almost completely digestible (98%) in the rumen. In addition, they are precipitated out of the cell wall by ethylene diamine tetra acetic acid (EDTA) which is contained in neutral detergent solution. A significant amount of pectin substances are contained in leguminous feedstuff fed to animals (e.g., alfalfa, soybean meal, beet pulp, etc.). These pectin substances may physically be associated with the cell wall, but chemically they are associated with and behave like cell solubles; therefore, they are also considered a part of the non-structural carbohydrates.
The major source of structural carbohydrates in dairy cattle rations is forage. The quality and degree of structural carbohydrate availability (digestability) to rumen microorganisms in different forages are quite variable, being influenced by such factors as plant variety, maturity at harvest and storage conditions. Grains generally have more non-structural carbohydrates and are generally less variable in carbohydrate content than forage.
It has been generally accepted that structural carbohydrate is a negative indicator of ration energy concentration. That is, the more structural carbohydrate a given ration contains, the less energy value it provides, and vice versa. Present energy-based feeding systems for ruminants are based on this relationship.
In order to develop a feeding system which includes regulation of carbohydrates in the total daily ration, it is necessary, of course, to have available an accurate and repeatable method of quantitating both structural and non-structural carbohydrates in each constituent of the ration. A procedure which has been used in the past to separate structural and non-structural carbohydrates involves refluxing a given sample in a neutral detergent solution and filtering out the insoluble portion, termed "neutral detergent fiber." It has been generally assumed that, for practical purposes, the netural detergent fiber could be equated to the structural carbohydrate portion of the sample and, conversely, the neutral detergent solubles were essentially the non-structural carbohydrate portion. However, the fractions of non-carbohydrate substances present in both the neutral detergent fiber and solubles are significant to a degree that a reliable regulated carbohydrate feeding program cannot be based upon such generalizations.
Another chemical procedure which has been used to quantitate total non-structural carbohydrate (TNC) utilizes an enzyme called Taka-Diastase. (see Smith, D. "Removing and Analyzing Total Non-Structural Carbohydrates From Plant Tissue." Wisconsin Agr. Exp. Sta. Res. Rep. 41, 1969). The procedure has also been modified, utilizing Bacillus subtilis type III A.alpha.amylase (see Madriz, J. M. S. Thesis, Cornell Univ., pp. 76, 77, 1981). These procedures basically involve the chemical action of enzymes on the plant material under consideration. Although theoretically measuring the total amount of non-structural carbohydrate in a sample, the enzyme dictates what is being digested and therefore what is being quantitated.
The Taka-Diastase enzyme is an .alpha.amylase derived from Aspergillus oryzae, an organism grown on sterilized wheat bran or rice hulls. This extracted enzyme represents more than 30 different enzymatic functions, and is not only amylolytic, but digests proteins and fats as well, according to Merck Index, 9th, Ed., p. 81, #633 (1976). Bacillus subtilis type III A enzyme has specific properties to hydrolyze, .alpha.1-4 glucosidic linkages of polysaccharides (starch), also according to Merck Index, supra. The activity of the latter enzyme may therefore be too "specific" to estimate all non-structural carbohydrates in a feedstuff. Therefore, non-structural carbohydrate measurements based on these enzymatic procedures are subject to variability and inconsistencies.
The principal object of the present invention is to provide a novel method of measuring the amounts of structural and non-structural carbohydrates in a given plant material.
Another object is to provide a method which is more accurate and reliable than previous, conventional methods for determining the structural and non-structural carbohydrate content of plant materials used as feedstuffs in cattle rations.
A further object is to provide an accurate and repeatable method for quantitating the structural and non-structural carbohydrate content of feedstuffs to permit formulation of dairy cow rations in a manner providing a positive response in milk production.
Other objects will in part be obvious and will in part appear hereinafter.